UScholar Works
 
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226 - 250 of 924
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CreatorTitleDescriptionSubjectDate
226 Williams, Clayton C.Scanning capacitance microscopy on a 25 nm scaleA near-field capacitance microscope has been demonstrated on a 25 nm scale. A resonant circuit provides the means for sensing the capacitance variations between a sub-lGO-nra tip and surface with a sensitivity of 1X 10 19 F in a I kHz bandwidth. Feedback control is used to scan the tip at constant g...Scanning capacitance microscopy1989
227 Ailion, David Charles79Br nuclear-quadrupole-resonance lineshape and Raman-induced spin-lattice relaxation in the incommensurate phase of β- ThBr4We performed 7 9Br nuclear-quadrupole-resonance (NQR) line-shape and spin-lattice relaxation time measurements in the incommensurate (D system j8-ThBr4 over the temperature range 293-2.5 K. In addition, we extended the theory of the effects of Raman processes on amplitudon and phason spin-lattice re...Spin-lattice; NQR; Raman process; Line shape; Phason gap; Incommensurate systems1989
228 Symko, Orest GeorgeMagnetic shielding and relaxation characteristics of superconducting YBa2Cu3O7 tubesHigh-7c superconducting tubes have been developed for magnetic shielding of SQUIDs at 77 K. The characteristics of such tubes show that adequate shielding exists for magnetic fields up to a critical field determined by the current density of the tube. Relaxation phenomena with two different time de...YBa2Cu3O7 tubes; High-Tc; SQUID1989
229 Williams, Clayton C.Lateral dopant profiling with 200 nm resolution by scanning capacitance microscopyMeasurement of dopant density in silicon with lateral resolution on the 200 nm scale has been demonstrated with a near-field capacitance technique. The technique is based upon the measurement of local capacitance between a 100 nm tip and a semiconducting surface. Lateral dopant imaging is achieved b...Dopant profile; Doping density; Scanning capacitance microscopy1989
230 Sokolsky, PierreEvidence for 10^18-eV neutral particles from the direction of Cygnus X-3Analysis of the cumulative Fly's Eye data reveals an excess of air showers from the direction of Cygnus X-3 at energies above 0.5 x 10^18 eV. No point source has previously been identified at such high energies. The probability of this excess arising as a chance clustering of isotropic cosmic rays i...Cygnus X-3; Extensive air showers; Neutral particles1989-01
231 Wu, Yong-ShiAbsence of (1,0) supersymmetry anomaly in world-sheet gauge theories: a purely cohomological proofA purely cohomological proof is given for the absence of the (1,0) supersymmetry anomaly in gauge theories on a world sheet. In particular, it is shown that generalized cohomological approaches to anomalies in supersymmetric gauge theory, either formulated in whole superconnection space or only in t...World sheet; String theory; Superfields; Superspace1989-01
232 Wu, Yong-ShiFast tracking detector with fiber scintillators and a position sensitive photomultiplierWe have studied the properties of a tracking detector composed of 32 fiber scintillators coupled to a multianode photo-multiplier placed in a pion beam at TRIUMF. We measured the efficiency of the detector, as well as its tracking capabilities and double hit resolution.Fast tracking detector; Fiber scintillators; Position sensitive photomultiplier1989-02
233 Wu, Yong-ShiRenormalization of the statistics parameter in three-dimensional electrodynamicsWe argue that the p function for the statistics parameter in (2+1)-dimensional electrodynamics is zero to all orders in perturbation theory beyond one loop. We show that there can be finite radiative corrections from massless charged scalar fields.Renormalization1989-02
234 Symko, Orest GeorgeNoise characteristics and instabilities of long Josephson junctionsIn a magnetic field, current biased long Josephson junctions exhibit the dynamics of fluxon motion which are affected by fluctuations. These consist of telegraph noise at voltage steps and instabilities due to chaotic behavior. Results on long junctions with McCumber number fic ranging from 10 to 10...Fluxon motion; Current biased; Instabilities; Telegraph noise; Perturbed sine-Gordon equation1989-03
235 Vardeny, Zeev ValentineTransient photomodulation spectroscopy of nanocrystalline hydrogenated siliconTransient photomodulation spectra were measured on nanocrystalline Si:H films in the time domain from 10-7 to 10-2 s, spectral range from 0.25 to 1.25 eV, and temperature range from 80 to 300 K. The properties of the spectra are compatible with the presence of two phases, amorphous and crystalline. ...Transient photomodulation spectroscopy; Nanocrystalline silicon1989-03
236 Symko, Orest GeorgeHigh Tc rf-biased SQUIDResults are presented on the behavior of a simple rf-biased SQUID made out of YBa2Cu307. It consists of a fractured ceramic pellet stuck together at room temperature. This simple device is shielded by a high Tc tube and it shows the characteristic flux quantization behavior up to 77K. At 4.2K its ma...High Tc RF-biased SQUID1989-03
237 Sokolsky, Pierre; Cassiday, George L.; Kieda, David B.Search for y rays above 10^14 eV from Cygnus X-3 during the June and July 1989 radio outburstsWe have looked for γ-ray emission above 100 TeV from the binary x-ray source Cygnus X-3 during a period of intense radio emission in the summer of 1989. We find no evidence for excess air showers from the direction of the source and the muon content of air showers from this direction is the same as...Cygnus X-3; Radio outbursts; Extensive air showers1989-11
238 Kieda, David B.; Cassiday, George L.; Sokolsky, PierreSearch for γ rays above 1014 eV from Cygnus X-3 during the June and July 1989 radio outburstsWe have looked for γ-ray emission above 100 TeV from the binary x-ray source Cygnus X-3 during a period of intense radio emission in the summer of 1989. We find no evidence for excess air showers from the direction of the source and the muon content of air showers from this direction is the same ...Fly's Eye1989-11
239 Vardeny, Zeev ValentineUltrafast electronic and acoustic effects in conducting polymersThe polarized picosecond pump and probe technique with 50 fsec resolution has been used to generate and detect electronic excitations and propagation of ultrasonic phonons in thin films of oriented and unoriented polyacetylene and polythiophene. We found that the photoexcitations are instantaneou...Ultrafast electronic effects; Ultrafast acoustic effects; Polarized picosecond pump; Pump and probe technique; Ultrasonic phonons1990
240 Ailion, David CharlesNMR determination of the Edwards-Anderson order parameter in the deuterated pseudo-spin glass Rb1-x(ND4)xD2PO4: anisotropy and concentration dependence of the ND4 deuteron second momentWe measured the rotationally averaged N D 4 + deuteron second moment in deuterated mixed single crystals Rb1_x(ND4 ) xD2P04 with x = 0.22, 0.44, 0.78, and pure ND4D2P04 . We found that the linewidths of the mixed systems show a strong dependence on the crystal's orientation with respect to the exter...NMR; Crystals; Deuteron second moment; Anisotropy; Linewidth1990
241 Vardeny, Zeev ValentineStudies of picosecond carrier dynamics in polysilane alloys: evidence for geminate recombination in small hydrogenated amorphous silicon clustersThe ultrafast photocarrier dynamics in polysilane alloys amorphous (SiH2)n' has been studied using the picosecond photoinduced absorption (PA) technique. For excitation below the optical gap, the PA response decays exponentially and is faster at low temperatures. This is interpreted in terms of e-h ...Picosecond carrier dynamics; Polysilane alloys; Geminate recombination; a-Si:H; Amorphous silicon; Ultrafast relaxation; Photoexcited carriers1990
242 Mattis, Daniel C.Dynamics of quasiparticles in the two-dimensional Hubbard modelThe Hubbard model at half-filling is a collective, antiferromagnetic insulator. We study added electrons or holes. The insulating energy gap and the dispersion of the added carriers are calculated variationally in two dimensions with use of a Monte Carlo evaluation of the electronic correlation f...Dispersion; Electrons; Carriers1990
243 Vardeny, Zeev ValentinePicosecond photomodulation study of nanocrystalline hydrogenated siliconWe have extended our photomodulation studies of nc-Si:H to the picosecond time domain. We measured the decays of photoinduced reflectivity with lOOfs temporal resolution as a function of. light intensity. Comparison with the data obtained on a-Si:H and c-Si indicates that ultrafast trapping and reco...Picosecond photomodulation; Nanocrystalline silicon1990
244 Williams, Clayton C.Lateral dopant profiling in MOS structures on a 100 nm scale using scanning capacitance microscopyScanning capacitance microscopy and atomic force microscopy have been used to image the extent of lateral dopant diffusion in MOS structures. The data are capacitance vs. voltage measurements made on a submicron scale. The technique is non-destructive when imaging uncleaved samples. New experim...Scanning capacitance microscopy; Dopant profiling1990
245 Wu, Yong-ShiImplications of a cosmological constant varying as R-2We advocate the possibility that the (effective) cosmological constant A varies in time as R- 2, R being the scale factor of our expanding Universe. This behavior can be obtained under some simple and general assumptions in conformity with quantum cosmology. After pointing out several advantages w...Cosmological constant1990-01
246 Kieda, David B.; Sokolsky, PierreSearch for > 200 TeV photons from Cygnus X-3 in 1988 and 1989Over a period of 16 months from April 1988 to August 1989, we have monitored the flux of cosmic-ray showers with energies above 2X 101 4 eV. We used a two-level array of scintillators covering an area of 3 X 104 m2. Counters on the surface measure the size and direction of each shower while counters...TeV photons; Cosmic ray showers1990-07
247 Wu, Yong-ShiSpace-time approach to holonomy scatteringA general concept of holonomy scattering is defined. It applies, among other things, to imply a nontrivial (generally, inelastic) scattering amplitude for the scattering of pure flux tubes off one another, when these fluxes are non-Abelian and do not commute. The amplitudes for such processes, as w...Flux tubes; Aharonov-Bohm scattering1990-07
248 DeTar, CarletonRole of baryons in chiral-symmetry restoration at high temperatureTo help provide insight into the apparent remarkable rise in baryon susceptibility at the high-temperature phase transition in QCD, we study the three-dimensional lattice SU(2) chiral model at finite temperature. The purpose of this study is to determine the extent to which a rising susceptibility i...Chiral model; Chiral symmetry; Quark plasma; Skyrmions; Phase transitions1990-07
249 Sokolsky, PierreSearch for > 200 TeV photons from Cygnus X-3 in 1988 and 1989Over a period of 16 months from April 1988 to August 1989, we have monitored the flux of cosmic-ray showers with energies above 2X 10^14 eV. We used a two-level array of scintillators covering an area of 3 X 10^4 m2 . Counters on the surface measure the size and direction of each shower while counte...Cygnus X-3; Extensive air showers1990-07
250 Vardeny, Zeev ValentineResonant-Raman-scattering studies of disorder in solution-cast polydiacetylene filmsThe disorder in polydiacetylene films cast from solution is studied by Raman scattering under preresonance and resonance conditions in both Stokes and anti-Stokes configurations. The disorder-induced inhomogeneities in the exciton energy levels and the strongly coupled vibrations cause strong disper...Polydiacetylene films; Stokes configuration1990-08
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